1. Field of the Invention
The present invention relates to an ignition timing control apparatus for controlling internal-combustion engine knocking.
2. Discussion of Background
An ignition timing control apparatus used in a conventional internal-combustion engine will hereinafter be described with reference to FIG. 11. In the drawing, a numeral 1 is an acceleration sensor mounted in an engine (not illustrated) for the detection of a vibration acceleration of the engine; a numeral 2 denotes a buffer amplifier which receives a signal from the acceleration sensor, and makes an impedance conversion of the signal, then outputting a signal; a numeral 3 represents an analogue gate for blocking a noise part of an output signal of the buffer amplifier which acts as an interference wave on knock detection; a numeral 4 denotes a gate timing controller which indicates the opening and closing of the analogue gate correspondingly to an interference noise generation timing; a numeral 5 denotes a noise level detector which detects the level of mechanical vibratory noise of the engine other than the engine knocking; a numeral 6 denotes a comparator which compares the output voltage of the analogue gate 3 with the output voltage of the noise level detector 5, then generates a knock detection pulse, a numeral 7 designates an integrator which integrates the output pulse of the comparator 6, generating an integrated voltage corresponding to a knocking strength, a numeral 8 denotes a phase shifter which shifts the position of a reference ignition signal in accordance with the output voltage of the integrator 7, a numeral 9 denotes a rotation signal generator which generates an ignition signal corresponding to present ignition advance characteristics; a numeral 10 denotes a shaping circuit which shapes an output waveform of the rotation signal generator 9, simultaneously controlling the circuit closing angle of power applied to an ignition coil 12; and a numeral 11 designates a switching circuit which interrupts power being fed to the ignition coil by the output signal of the phase shifter 8.
FIG. 12 shows the vibration frequency characteristics of this engine. In this drawing, a character A indicates the frequency characteristics without occurrence of knocking, and a character B with knocking. This engine vibration includes, beside a knock signal (a signal generated along with knocking), mechanical noise of the engine. In FIG. 12, it is understood from a comparison between A and B that the knock signal has peculiar frequency characteristics. Therefore, its distribution differs with an engine used or with a difference in the mounting position of the acceleration sensor, and besides, in either case, there is a distinct difference with the presence or absence of engine knocking. It is, therefore, possible to control other frequency components and efficiently detect the knock signal by detecting the vibratory acceleration of the engine by the acceleration sensor 1 having a natural vibration frequency plus the frequency components of the knock signal.
FIGS. 13 and 14 show the operation waveform of each part of the conventional device of FIG. 11. FIG. 13 shows the mode of engine operation without knocking, and FIG. 14 shows the mode of engine operation accompanied by knocking. The operation of the conventional device shown in FIG. 11 will be described with reference to FIGS. 13 and 14. The ignition signal produced by the rotation signal generator 9 is shaped by the shaping circuit 10 to an opening-closing pulse having a desired circuit closing angle correspondingly to the ignition timing characteristics preset in accordance with the engine speed. The switch circuit 11 is driven through the phase shifter 8, thereby interrupting the power feed to the ignition coil 12. The engine is ignited by ignition voltage of the ignition coil 12 that is generated when the current is interrupted, thus being operated. Engine vibration occurring during engine operation is detected by the acceleration sensor 1.
When the engine is not knocking, no engine vibration by knocking is generated. However, a mechanical noise shown in FIG. 13(a) appears in the output signal of the acceleration sensor 1 due to the presence of other mechanical vibration. This mechanical vibration is selectively changed into an electric signal by the acceleration sensor 1 having the natural vibration frequency plus the knock signal frequency.
The mechanical noise component of this signal is controlled considerably as shown in FIG. 13(b). However, the ignition noise component, or an electric noise overlapping therewith, being powerful, is outputted at a high level. In this case, it is likely that the ignition noise is mistaken for a knock signal, and therefore the analogue gate 3 is closed for a period of time from an ignition timing by the output (FIG. 13(c)) of a gate timing controller 4 which is triggered by the output of the shape shifter 8, interrupting the ignition noise. In the output of the analogue gate 3 only a low-level mechanical noise will remain as shown at C of FIG. 13(d).
In the meantime, the noise level detector 5 is designed to respond to a change in the peak value of the output signal of the analogue gate 3. In this case, the noise level detector 5 has the characteristics capable of responding to a relatively mild change in the peak value of normal mechanical noise, producing a slightly higher dc voltage than the peak value of the mechanical noise (D of FIG. 13(d)).
Therefore, since the output of the noise level detector 5 is greater than a mean peak value of the output signal of the analogue gate 3 shown in FIG. 13(d), the output of the comparator 6 which compares them is not produced as shown in FIG. 13(e), with the result that all the noise signal is eliminated.
With the output voltage of the integrator 7 remaining at zero as shown in FIG. 13(f), a phase angle (a phase difference of input and output in FIGS. 13(g), (h)) will become zero.
Therefore, the opening-closing phase of the switching circuit 11, or the power interruption phase of the ignition coil 12, which is driven by this output, will become of the same phase as the reference ignition signal of the output of the shaping circuit 10, the ignition timing becoming the reference ignition timing.
When knocking has occurred, the output of the acceleration sensor 1 includes a knock signal in the vicinity of a time delaying from the ignition timing as shown in FIG. 14(b); the signal that has passed the analogue gate 3 comprises a mechanical noise largely overlapped by a knock signal as shown in FIG. 14(d).
Of the signal that has passed through this analogue gate 3, the knock signal rises sharply, and therefore the output voltage level of the noise level detector 5 delays responding to the knock signal. In consequence, the input of the comparator 6 will become as shown in C and D of FIG. 14(d), and therefore there is generated a pulse with the output of the comparator 6 as shown in FIG. 14(e).
The integrator 7 integrates the pulse thereof, generating an integration voltage as shown in FIG. 14(f). Since the phase shifter 8 shifts towards the time delay side the output signal (FIG. 14(g) (Reference ignition signal)) of the shaping circuit 10 in accordance with the output voltage of the integrator 7. The output of the phase shifter 8 delays shifting phase as compared with the phase of the reference ignition signal of the shaping circuit 10, driving the switching circuit 11 in phase shown in FIG. 14(h). Consequently, the ignition timing delays, with the result that knocking is restrained. The repetition of these conditions shown in FIGS. 13 and 14 achieves the optimum ignition timing control.
Subsequently, the acceleration sensor 1 will be explained with reference to FIG. 15. In this drawing, a numeral 21 denotes a metal base provided with a screw section 21a for mounting this vibration detector to a part to be detected, for holding a vibration detecting section described below. A numeral 22 is a metallic diaphragm comprising a vibration detecting section together with a piezoelectric element 22 which transforms vibrations into an electrical signal; a numeral 24 is a lead wire for leading out the detection output of the piezoelectric element 23, a numeral 25 represents a molded plastic cover joined with the base 21 for closing the vibration detecting section, at a caulked section 21b of the base 21, a numeral 26 expresses a terminal, which is installed integral with the cover 25 by an insert molding method, for leading the detection output out of the detector. A numeral 26a denotes a locking piece, which is a part of the terminal 26 bent to lock the cover 25 from accidental removal and rotation. The diaphragm 22 and the piezoelectric element 23 are joined together with an electrically-conductive adhesive and therefore an electrode on the bonded side of the piezoelectric element 23 becomes of the same potential as the base 21.
Next, an explanation will be made on detecting operation. This detector is mounted to the part to be detected, by tightening the threaded section 21a of the base 21 and will receive vibration. This vibration passes to the diaphragm 22 joined at the caulked section 21a of the base 21. This diaphragm 22, together with the piezoelectric element 23, has a good sensitivity, quickly responding to the vibration of preset natural vibration frequency and applying distortion to the piezoelectric element 23. The piezoelectric element 23 outputs an electric signal corresponding to the distortion with reference to the electrode on the joined surface side, detecting vibrations as an electric signal. This electric signal is led out of the detector through the lead wire 24 and the terminal 26.
In the conventional knocking control device of an internal-combustion engine as described above, there was a problem that various troubles of signal lines in the acceleration sensor 1 or between the sensor and the buffer amplifier 2 can not easily be detected.
Next, this problem will be described by referring to FIG. 16. In this drawing, numerals 2, 23 and 26 designate the buffer amplifier, the piezoelectric element and the terminal respectively. A numeral 2a denotes an input terminal (the input terminal of the knock control circuit) of the buffer amplifier 2; a numeral 2b expresses an amplifier comprising the buffer amplifier 2; a numeral 31 represents a signal line installed between the terminal 26 and the input terminal 2a of the acceleration sensor 1 to input the detection signal to the amplifier 2b; a numeral 32 is a resistor connected between the input terminal 2a and the circuit power source of the buffer amplifier 2; a numeral 33 is a short-circuit line between the signal line 31 and the ground; and a numeral 34 is a circuit-opening point produced to open the signal line 31.
In FIG. 16(a), the detection signal from the piezoelectric element 23 which shows a normal state is outputted through the terminal 26, being inputted to the input terminal 2a of the buffer amplifier 2 through the signal line 31. In the meantime, since the resistor 32 is connected between the circuit power source and the input terminal 2a, the bias is being applied to the piezoelectric element 23 from the input terminal 2a through the signal line 31. Here, the piezoelectric element 23 functions as an electric element capacitor, and therefore all of the input terminal 2a, the signal line 31 and the terminal 26 are applied with the circuit power voltage.
FIG. 16(b) shows the buffer amplifier circuit shorted to the ground (for example a short-circuit between the electrodes of the piezoelectric element 23) of the same potential as the terminal 26 of the acceleration sensor 1 or the signal line 31 shorted to the ground. That is, this drawing shows a trouble that a shorted line 33 has occurred, shorting the signal line 31 to the ground. In this case, the input terminal 2a is shorted to the ground, the occurrence of a trouble being detected from a change in the input potential of the buffer amplifier 2. Accordingly, when the electric potential at the input terminal 2a is decreased to the ground potential, or lower than a specific voltage, by the fail detection circuit, which is not illustrated, a fail signal must be generated. This fail signal drives for example the integrator 7, retarding the ignition timing in order to prevent the occurrence of knocking and accordingly enabling safe operation of the engine without knocking in the event that knocking can not be detected.
FIG. 16(c) shows a disconnection (open circuit) in a section of the same potential as the terminal 26 in the acceleration sensor 1, or disconnection of the signal line, or the opening of the connector circuit used for their connection. Now the disconnection of the signal line 31 is shown.
Since the piezoelectric element 23 is a capacitor, the electric potential at the input terminal 2a in this case will not vary from the circuit power supply voltage of the buffer amplifier 2. Namely, no abnormality can be detected.
It, however, is seen from our experience that a trouble most frequently experienced in the market is the opening of a circuit caused by this disconnection.
The ignition timing control device of the internal-combustion engine shown in FIG. 17 is also a known art. This device is identical to the conventional device shown in FIG. 11 except for the use of a frequency filter 72 in place of the buffer amplifier 2. The frequency filter 72 allows the passage of the part of the output signal of the acceleration sensor 1 that is sensitive to knocking. The operation waveform of each constitutive part of the device and the vibration frequency characteristics of the engine both shown in FIG. 17 are the same as those shown in FIGS. 12 to 14 and therefore are not described hereinafter. In FIG. 17, a numeral 70 denotes a knock detecting section including members from the frequency filter to the integrator.
Generally, in the internal-combustion engine, knocking is likely to occur on starting or during acceleration. Under other operating conditions, or in a no-control range, no knocking occurs. In most cases, the engine is normally operated in the no-control range, and accordingly the knock control section remains stationary. The integrator 7 in FIG. 17 is in its normal reference state of operation when not producing an output. That is, under most of its operating conditions the integrator 7, when normal, does not output. It is, therefore, difficult to judge from this output whether the integrator 7 is normal or abnormal, that is, whether the knock detecting section 70 is normally operating.
In the meantime, since factors generating the knocking vary in the knock control range, it is not easy to judge, only from operating information used for detection and control, whether or not each part is in a desired normal condition.
If the knock detecting section 70 is malfunctioning, no proper knocking control can be effected, sometimes resulting in a failure of the engine. The malfunctioning of this device is very dangerous.
The conventional ignition timing control device of internal-combustion engine has such a problem that if the operating condition of the knock detecting section can not easily be confirmed or the knock detecting section is malfunctioning, no desirable knock control can be achieved, resulting in worsened feeling caused by knocks, an engine failure, degraded merchantability, a functional loss, and further in a danger to induce a fatal accident.